The overall aim of this project is to develop two PET cameras whose geometries are optimized for detecting breast cancer. These post- x-ray mammography tools would determine whether suspicious lesions have the increased metabolism associated with breast cancers, and have the potential to provide a cost effective, non-invasive alternative to biopsy. FDG is an excellent tracer for breast cancer with >90 percent specificity and sensitivity, as measured with conventional PET imaging for lesions >1 cm. We believe that the higher solid angle coverage and spatial resolution of these specialized cameras will allow them to push the minimum tumor size needed to achieve this high diagnostic accuracy to well below 1 cm diameter. These high performance cameras contain a much smaller volume of detector, which could reduce the camera cost by a factor of 10 compared to conventional PET and so make the technology more readily available to patients. Our two geometries place PET detector modules in close proximity to the breast (similar to a mammography unit). One geometry is rectangular and completely encircles the breast while the other is a pair of parallel planes. These geometries improve the sensitivity and the spatial resolution significantly compared to a conventional PET camera; the sensitivity increases by a factor of 30 for the rectangular and 20 for the parallel plane geometry, while the spatial resolution increases by a factor of 2 for both geometries. We predict that this will allow rapid identification of cancerous lesions for structures down to 5 mm in diameter, possibly even with a small (<1 mCi) injected dose of FDG (which is 10 times less than that used in current studies). In the past 6 years we developed the core camera components, including a high performance PET detector module capable of measuring the depth of interaction within the crystal and the necessary readout electronics. As the construction is virtually complete, the present project focuses on commissioning the PET cameras, developing calibration routines and reconstruction algorithms for these unique camera geometries, characterizing the imaging properties with phantoms, and preliminary evaluation of the imaging properties in patients. These cameras are designed specifically for breast cancer, but the detector module developed could also be incorporated into other high resolution PET camera geometries, such as a high-resolution high-sensitivity human brain imager or a small animal (mouse) scanner with extremely high sensitivity. These designs, when complete, will be offered to private industry to incorporate into commercial instruments.